1. Field of the Invention
The present invention relates to an apparatus for connecting a bare semiconductor die having a size and bond pad arrangement, either solder ball arrangement, or pin arrangement (hereinafter referred to generally as a "terminal arrangement"), which does not conform to a printed circuit board with a specific or standardized pin out, connector pad, or lead placement (hereinafter referred to generally as a "connection arrangement"). More particularly, the present invention relates to an intermediate conductor-carrying substrate (hereinafter referred to generally as an "adaptor board") for connecting a non-conforming bare die to another printed circuit board having a given connection arrangement (hereinafter referred to generally as a "master board").
2. State of the Art
Definitions: The following terms and acronyms will be used throughout the application and are defined as follows:
BGA--Ball Grid Array: An array of minute solder balls disposed on an attachment surface of a semiconductor die wherein the solder balls are refluxed for simultaneous attachment and electrical communication of the semiconductor die to a printed circuit board.
COB--Chip On Board: The techniques used to attach semiconductor dice to a printed circuit board, including flip chip attachment, wirebonding, and tape automated bonding ("TAB").
Flip Chip: A chip or die that has bumped terminations spaced around the active surface of the die and is intended for facedown mounting.
Flip Chip Attachment: A method of attaching a semiconductor die to a substrate in which the die is flipped so that the connecting conductor pads on the face of the die are set on mirror-image pads on the substrate (i.e. printed circuit board) and bonded by refluxing the solder.
Glob Top: A glob of encapsulant material (usually epoxy or silicone or a combination thereof) surrounding a semiconductor die in the COB assembly process.
PGA--Pin Grid Array: An array of small pins extending substantially perpendicularly from the major plane of a semiconductor die, wherein the pins conform to a specific arrangement on a printed circuit board for attachment thereto.
SLICC--Slightly Larger than Integrated Circuit Carrier: An array of minute solder balls disposed on an attachment surface of a semiconductor die similar to a BGA, but having a smaller solder ball pitch and diameter than a BGA.
State-of-the-art COB technology generally consists of three semiconductor dies to printed circuit boards attachment techniques: flip chip attachment, wirebonding, and TAB.
Flip chip attachment consists of attaching a semiconductor die, generally having a BGA, a SLICC or a PGA, to a printed circuit board. With the BGA or SLICC, the solder ball arrangement on the semiconductor die must be a mirror-image of the connecting bond pads on the printed circuit board such that precise connection is made. The semiconductor die is bonded to the printed circuit board by refluxing the solder balls. With the PGA, the pin arrangement of the semiconductor die must be a mirror-image of the pin recesses on the printed circuit board. After insertion, the semiconductor die is generally bonded by soldering the pins into place. An under-fill encapsulant is generally disposed between the semiconductor die and the printed circuit board to prevent contamination. A variation of the pin-in-recess PGA is a J-lead PGA, wherein the loops of the J's are soldered to pads on the surface of the circuit board. Nonetheless, the lead and pad locations must coincide, as with the other referenced flip chip techniques.
Wirebonding and TAB attachment generally begins with attaching a semiconductor die to the surface of a printed circuit board with an appropriate adhesive. In wirebonding, a plurality of bond wires are attached, one at a time, from each bond pad on the semiconductor die and to a corresponding lead on the printed circuit board. The bond wires are generally attached through one of three industry-standard wirebonding techniques: ultrasonic bonding--using a combination of pressure and ultrasonic vibration bursts to form a metallurgical cold weld; thermocompression bonding--using a combination of pressure and elevated temperature to form a weld; and thermosonic bonding--using a combination of pressure, elevated temperature, and ultrasonic vibration bursts. The die may be oriented either face up or face down (with its active surface and bond pads either up or down with respect to the circuit board) for wire bonding, although face up orientation is more common. With TAB, metal tape leads are attached between the bond pads on the semiconductor die and the leads on the printed circuit board. An encapsulant is generally used to cover the bond wires and metal tape leads to prevent contamination.
Although the foregoing methods are effective for bonding semiconductor dies to printed circuit boards, the terminal arrangements of the dies and the connection arrangements of the boards must be designed to accommodate one another. Thus, it may be impossible to electrically connect a particular semiconductor die to a printed circuit board for which the semiconductor die terminal arrangement was not designed to match the board's connection arrangement. With either wirebond or TAB attachment, the semiconductor die bond pad may not correspond to the lead ends on the circuit board, and thus attachment is either impossible or extremely difficult due to the need for overlong wires and the potential for inter-wire contact and shorting. With flip chip attachment, if the printed circuit board connection arrangement is not a mirror-image of the solder ball or pin arrangement (terminal arrangement) on the semiconductor die, electrically connecting the flip chip to the printed circuit board is impossible.
Therefore, it would be advantageous to develop an apparatus for connecting a semiconductor die having a size and bond pad arrangement, solder ball arrangement, or pin arrangement ("I/O pattern") which does not conform to a printed circuit board with a specific or standardized pin out, connection pad location, or lead placement ("I/O pattern").